Marvelous Flash
by destinybroughtme
Summary: Together with a visitation of an old friend, Caitlin found herself in a situation that is very other worldly.
1. Chapter 1

**A/N: Hey there! This is my first time writing a full length story and it is a crossover. This story is slight AU, I think. Enjoy some FitzSimmons and SnowBarry!**

* * *

Fitz is on an off from field and visiting an old friend. Technically, surprising her with his presence. He has never seen her for almost a year. The last time he saw her was devastating.

Her fiancée died in an accident.

* * *

Caitlin was preparing her purse when someone suddenly knock on her front door. "Coming!" she announced to whoever it is on the other side of the door. She opened it and can not believe what her eyes were seeing. "Oh my God Fitz!" she hugged him tightly. "Well, hello to you too Caitlin," he said out of breath. "Come in."

* * *

Caitlin called her colleagues at STAR Labs. She told them that she won't be able to go to work today.

There they were talking about nonsense.

Fitz told her some adventures he had like when he met Sif the godess of war who also happens to be a companion of Thor. Caitlin told him if he also had seen Thor if he really is that built, how tall was he, was he dreamy, which Fitz laughed at and politely said no.

In the middle of their conversation, Caitlin suddenly asked, "Where's Jemma?" 'She just really needs to ask that didn't she.' Fitz thought.

"She's uh, she's at work," Fitz lamely replied which gained him a suspicious look from Caitlin. She didn't pry though. She knows that he will tell her whenever he is ready.

* * *

Back at STAR Labs, Cisco was repairing the torn suit that Barry wore the other day. He was also adding features when suddenly Barry whooshed his way in. "Hey, Cisco!" he greeted. "Oh hey, look at this, do you think adding Kevlar would be comfortable while you're running. i mean, it would lessen your injuries but it may also cause-" "Yes Cisco, I think its fine." Barry interrupted him from rambling. "Okay!" Cisco went back at his work. That was when Barry noticed.

"Where's Caitlin?" he asked.

"She said she won't be able to come to work today." Dr. Wells answered him while wheeling his way to them. "And why's that?" he asked again. "She didn't really tell," Cisco answered without elaboration. "Look, Barry Caitlin rarely takes a day off but when she does, it is an important matter," told him and he just nodded.

"Now let us test your speed again."

* * *

Barry knows that he shouldn't be worried. But the fact that Caitlin rarely takes a day off would not leave his mind so he decided to go to her house.

He was strolling when he saw that her lights were open. He knocked on the door and waited for her.

* * *

Caitlin was about to bring up the subject again after Fitz explained his invention the night-night pistol, when someone knocked on her door again. Caitlin stood up and answered the door. "Barry." "Hey Caitlin, may I come in?" "Sure."

"So what brings you here?" she asked him. "Uh-" Barry was about to reply when he saw someone in Caitlin's kitchen. "Who is he?" he asked. "Oh. Barry this is Leo Fitz and Fitz this is Barry Allen." she introduced them to each other. They shook each other's hands and sat down on her sofa.

They talked about their occupation (which both were careful not to spill anything). Schools they attended. Favorite food, color and everything. Barry starts to like the guy for he manages to catch every references he made about tv shows and movies. Fitz also cracked jokes he understood. He could see clearly why Caitlin enjoyed his company.

Caitlin went to the kitchen to prepare them dinner.

"I just wish I brought Jemma with me. She's more fun than I am." Fitz suddenly droppped the bomb.

From that moment Barry saw that even though Fitz was there, his mind was elsewhere.

He suddenly asked, "Who's Jemma by the way?' and quickly covered his mouth. "It's okay." Fitz laughed at Barry's actions. He then took a deep breath. "She's uh, my best friend. or was." Barrry must have had a confused look so Fitz tried to elaborate. "Well it's complicated." Barry understood what he meant. The words left unspoken was clear to him.

"Hey guys! Do you want to eat or not? I made Carbonara."

They made their way to the dining room.

"So Caitlin." Fitz starts. "Hmm," she looked at him questioningly. "I would be truthful to you. In the past months, I was suffering from Hypoxia. It was hard for me to speak. I-I can't say the exact word I wanted to say. My hand also was damaged. You may have noticed that- that I stutter every time. A-a-and i know it's all confusing. God i just wanted to tell you everything b-but I can't."

Caitlin went by his side soothing his back comfortingly.

He continued telling his story from where he was in a pod with Jemma. He confessed his feelings. How he didn't give her time to process things. How he saved her life. Some he left unexplained.

He really could not explain everything to them. He can't say that he and Jemma are agents of S.H.I.E.L.D. when it is believed to be gone. He can not tell that they are fighting off bad guys called Hydra and out of this world things and creatures. In short, he can not explain how they got there in the first place.

* * *

"Hello, Sir. What is it about?" he asked Coulson on the other line. "Where were you going again?" Coulson asked him. "Confused about his answer Fitz said, "Central City sir. Excuse me, sir, but is there a problem?" "Actually yes. You remember Donnie Gill?" "Uh yes." "He's alive and I believe he's making his way to where you are now."

* * *

**A/N: I'm not really a great writer but I hope you enjoyed this chapter.**


	2. Chapter 2

**AN: Hey everyone I'm back! I changed the ending of chapter 1 because I find it difficult to have and continue with Lorelei. Read it first before continuing this chapter. I just want to share with you this fantastic video of Fitzsimmons and Snowbarry. watch?v=tna_BtWpiaE** **Now go watch** **it! It's a-m-a-z-i-n-g!**

"Wha-what do you mean? He's back?" Fitz asked hearing while still working on believing. "Yes." "Sir where do we meet." "The Central Park. See you there in 30." Coulson ended the call.

* * *

_At the bus..._

"Simmons!" Skye called from behind. Jemma turned around to face her. "I know it must have been difficult for you since the last time you saw him-" "It's okay Skye. You did that to protect me." Simmons smiled but she knows that it gave her away. She finds this whole new world of them cruel. Skye was different. Coulson was different. Ward, who saved her from falling off a plane,a man she trusted a lot, turned out to be the enemy. Triplett, sweet Triplett. He didn't need to perish. Fitz. Her Fitz may never be the same anymore. As much as she would like to, things will never be the same ever again because she too, changed.

That seems to be the only constant thing in the world.

* * *

"Caitlin! Barry!" Fitz called the two. "What is it?" Caitlin asked. "I-it's hard to explain right now but I need your help." Fitz said pleadingly. "It's fine with me." Barry answered before Caitlin opened her lips. "As long as it does not involve shooting,' he added which made Caitlin smile and Fitz's chest heavy. So he exhaled loudly. "Let's just go to the Central Park. Shall we?" "Yeah." "Sure." Caitlin and Barry said at the same time.

* * *

"Bobbi you're up! I need you to fly the aircraft. We're fetching Fitz. Skye you come with us." Coulson demmanded. "I think Skye should stay here, I'll come to your aid instead. She needs to rest," May stopped him from walking away. "I would be out in the open. That is why I need you here. They need a leader in case I'm not around," Coulson retaliated to which May obeyed. "Be careful out there," was the last thing she said to the three of them.

* * *

_At the park... _

"So why are we here Fitz," Caitlin asked. "Um-"

Before he could even answer the aircraft came by them.

Barry swore he saw it go out in stealth mode. He remained to be astonished. The pad opened.

"Sir I brought friends with me." Fitz said as they entered. "How do you know that, Agent Fitz?" Coulson asked. He stares at the strangers while both are unaware. With Caitlin, it's because of confusion. '_Agent Fitz. Agent Leopold Fitz. What does that even mean? is Jemma an agent too?' _She asked to no one, really. With Barry it's because of amazement. He's like a kid in a candy store.

"This is Barry Allen. He works at Central City Police Department as a forensic scientist. This is Caitlin Snow. She's a geneticist. Sir I-I believe we need their help," Fitz pleaded then looked to Skye for support. She looked away. She finds it hard to trust anyone. Make that two strangers. Especially the man. She can not explain why but she feels he is hiding something.

"We do need their help but are you sure they will help us?" Coulson asked.

Fitz looked to both of them. Barry nodding madly and Caitlin with wide eyes.

"I-um I tink we need to talk for a second," with that Caitlin dragged Barry away from them.

"Are you crazy!" Caitlin whispered-shouted. "This can be dangerous." she added. "Caitlin they're good guys! Bad guy doesn't fit Fitz nor Jemma Simmons from what you both told me," Barry said. "Yeah well they kept this secret to me for almost a decade," she debated. '_She's got a strong point._' Barry thought but he feels this is what they were supposed to do. "Don't you want to help people? Protect them? Because I'm sure that's what I read in their manual right there. It's what they do," Barry pointed at the booklet behind him which is 3 meters away. "Fine then."

They went back to Coulson, Skye and Fitz. "We're happy to help sir," Barry offered his hand to which Coulson shook. "I'm keeping an eye on them," Skye offered.

She then sat in her respective seat as the two make themselves comfortable.

She searched for news in Central City and one thing that captured her is the impossible. The Flash.

"We're going to the Bus. Make yourselves comfortable. We need your help to save our lost fellow. Donnie Gill," Coulson informed the visitors.

Fitz eyes were saddened by the mere mention of his name. He blames himself for what happened to him.

"Sir when do you think Donnie arrives at Central City?" Fitz asked. To which Coulson replied, "Two days from now on." "How do you even know that he's coming to Central City?" he again asked. "Because he heard about a man who shoots people with ice." Coulson replied. Caitlin and Barry looked at each other with wide eyes but remained silent.

"Thank God it's Friday?" Barry asked. "Oh yeah, I do not need to lie to Cisco and Dr. Wells about this. Thank God it's Friday!" Caitlin whispered back.

* * *

**AN: I hope you like that! I've got a hard time continuing this story because I have another one in mind. I may publish that story sooner.**


	3. Chapter 3

**A/N: A reminder guys... This story occurs after episode 10 of both shows.**

* * *

"We're touching in 5," Bobbi reminded them.

Skye is still reading about this "Streak" that saves people. Most says that he appears and goes in a blink like viola! She still finds it intriguing how this city have supers. The team have been so busy with the Obelisk and the _city _to focus on other things.

Right now though, nothing seems to surprise her anymore.

Everyone's silent during the whole trip. No matter how badly Caitlin wants to ask Fitz about everything.

"We've touched down. You guys can come down now."

And they did one by one.

Simmons and May are waiting for them to climb down. Simmons hugged Skye and May gave a smile or something that was close to it.

"Who are they?" May asked, the first to notice that they came back with company. Simmons pulled away from Skye. Realization dawns on her. "Caitlin!" she hugged her. "Oh Jemma, it's been so long," Caitlin returned her hug. "You owe me an explanation" Caitlin tells her. "No. Lots and lots of explanation." she corrects herself after looking around.

The two pulled away. Simmons flashed a smile on Fitz. He gave her a nod.

"Barry this is Jemma Simmons. Jemma this is Barry Allen," Caitlin introduced them. They shook hands. "And this is agent May," Simmons introduced her to the new comers.

"Simmons. Show them around the lab," Coulson commands.

"Sir, it would be my genuine pleasure."

They made their way to the lab.

* * *

_At the lab..._

"This is where I work. We've got everything that you would be needing. Well, more at base but the bus is pretty much packed." Simmons tours them. "Why is Fitz not with us?" Barry asked.

_'He just really needs to ask that right?' _Jemma says in her head.

"Oh uh um, he said he wanted to be assigned at the garage. He thinks it is for the best. At first I didn't like the idea but since Mac is still recovering, I think it's for the best too." she replied.

Skye then walked into the lab.

"You two owe an explanation. Your city seems to have supernatural happenings. First, a man who turns to steel. Much like Carl Creel." Skye looked over at Simmons for a second. "Except he can duplicate physical properties of anything he touches or touches him," Jemma added. "And then there's this Flash." Skye continues. "I believe you know him, Caitlin." says Skye.

Barry and Caitlin then, tenses up. "He saved me once. No. I correct myself he always saves me and our city." Caitlin answers her.

"Okay. But you still didn't explain anything." Skye pursues.

"I am working for S.T.A.R. labs when the particle accelerator exploded. It turned people- made them meta-humans. Humans that are capable of doing something that the rest of us could not," Caitlin told her.

"Thank you for being honest with me." Skye said which gained a confused look from Caitlin and Barry. "I knew what happened. I was just testing you."

She left.

"What was that all about?" Barry asked.

"She has been through a lot lately. Please try to understand. She's having trouble with people right now after the incident."

They didn't ask for what happened. Based on Skye's actions, they decided that it is best to leave the matter alone and focus at the task at hand.

"So, Donnie Gill, how did he get his ability?" Caitlin asked.

"I believe he got his freezing ability after he got hit by a lightning while trying to shut down his research which is a freezing technology."

"Abilities gained after he was hit by lightning. Right." Barry said.

Caitlin and Barry looked at each other.

"We just need to formulate dendrotoxin that would be strong enough to handle him."

"That's easy!" Caitlin answered way too quickly. She earned a look from Barry and a raised eyebrow from Jemma.

"I mean we just have to double the -"

"But how are you sure that that would not-"

"I think it's just right. I mean, given his body temperature-"

"Guys! Let's just double the effect of the I.C.E.R. and give it a go." Barry said silencing the two of them.

"We're going to need Fitz." Caitlin told Jemma.

"Yeah. I-I'm going to fetch him."

* * *

_At the garage..._

"Ho-how are you Mack?" Fitz asked arranging the tools he needs for fixing his DWARFs not really looking at him.

"I don't really know. It's like a part of me was stolen and replaced by something unimaginable. Something foreign. Something alien."

Fitz looked up to see him in a trance. He was lost again, in his whole little world.

"I was doing things that are against my will. I almost hurt you guys-"

"Don't do that to yourself. Look. Look. What what you did was- what was the word again? I-it was out of your control. You are not to blame for your actions down there. Please stop loathing yourself for something like that"

There was a knock on the door.

It was Jemma.

"Uh Fitz, can I borrow you for a while? We need your help regarding the I.C.E.R."

"Yeah. Yeah Sure." Fitz said still looking at Mack.

Jemma left not really feeling comfortable.

"I'll be back."

With that Fitz took off.

* * *

**A/N: I'm so sorry for posting just now. I'm terrible at updating. It's just that I'm having so many ideas that are not relating to this story and the shows are great that it's kinda hard to write an au. But anyway, I'll be updating as soon as I can but I'll probably write a oneshot before writing the next chapter. I totally gave a Clintasha moment there between Fitz and Mack.**


	4. Chapter 4

**A/N: I'm so sorry for not posting for months. I've been really busy plus I am on instagram too. I will really try to write more now. I'm just looking for an inspiration, I guess. Anyways, here's Chapter 4! Please forgive me for any mistakes I'll be making. I'm a bit rusty.**

* * *

The four of them successfully formulated an I.C.E.R. enough to handle Donnie (theoretically) to take him to a (what Skye told Barry and Caitlin ) classified location.

"I really like this I.C.E.R., can I keep one?" Caitlin asked Jemma.

"Yes of course. I've heard the stories about your city. I think it's fine that you keep one for yourself."

"Thank you Jemma."

Barry looked worried. He knew why Caitlin would want something that she can use to protect herself. It has been two weeks since that happened but he understood. He just couldn't bear to think that he was the reason for it.

Fitz could read his _concern_ as clear as day but he did not say anything about it.

Coulson got in with an unreadable face.

"We've got eyes on him. He's at a coffee shop in Central City."

"Which one exactly?" Barry asked.

"Jitters." May said walking in.

"I may need you both on that quinjet now. Fitz, you're coming with us." Coulson ordered around.

Fitz was already on his feet.

"Sir-"

"You'll stay here Simmons. I know that the last time you two have seen each other was unpleasant that's why Skye is not coming with us too."

* * *

_At the quinjet..._

"Sir my bestfriend works there." Barry told Coulson.

"Oh. I suppose you should warn your bestfriend about Donnie." Coulson replied.

"But sir, how will she be able to believe what I say?"

"If she truly is a dear friend, she'll listen."

And somehow that hit him really hard.

Fitz, who heard the entire conversation, was also hit by the statement.

"I hope you're all set. We're almost there." May informed them from the cockpit.

Barry pulled out his phone. His phone is ringing loudly in his ears.

_'Come on Iris. Pick up. Pick up.'_

_"_Hey Barry what's up?"

_"Iris I need you to listen to me. How long is it after your shift?"_

_"_Fifteen minutes. Why Bar? What's wrong."

_"I need you to follow what I say. Okay?"_

_"_Yeah."

_"Right after your shift and I mean right after get out of there okay?"_

"Okay."

_"Be safe"_

He hung up.

"She'll be fine Barry." Caitlin said from behind him.

"Sorry. It's just- sometimes I feel like everyone close to me is getting hurt because of me."

"Hey! That's not true."

"It was my fault why Snart and Rory kidnapped you."

"Did you force me to stay at S.T.A.R. Labs after the particle accelerator exploded?"

He shook his head.

"Did you ask for me to stay when you started helping people?"

"No."

"See? It was my decision. I chose this path Barry. I know that in this line of work nothing is ever easy but I am willing to do it. I've felt what it was like to loose someone you love. And if there's a chance that I could help people not to experience what I had every day? I would do it. Even if my life's at stake."

There was a moment of silence between them.

"Guys, we're here." Fitz informed them.

It was two blocks away from Jitters.

They started walking and Barry prayed that Iris would be out and the store would be closed when they get there.

* * *

Iris was just finishing cleaning tables. Her co-worker Meg is still sweeping the floor. There was only one costumer left with his Iced Caramel Macchiato still untouched.

Iris felt sorry for the guy. Maybe he got stood up or rejected or anything bad happened to him because he looked down in the dumps.

"Sir. We are closing in 5 minutes." Meg informed the costumer.

"Yeah. I'll just wait outside."

He stood up with his drink in hand and got out.

"I feel sorry for him." Meg said when he's out of earshot.

"Yeah me too." Iris said while washing her hands.

"Let's go!" Meg led her outside.

* * *

On their way home, Iris looked for her phone in her bag but it wasn't there.

"Hey, Meg."

"Hmm?"

"I think I forgot my phone at the Jitters."

"Oh, then let's go get it." she offered.

"No. It's okay. We're almost at your apartment. I'll just go get it myself." Iris assured her.

"Alright. Just text me when you get home. Bye." Meg waved at her.

She waved back.

"Bye."

* * *

"Are there any civilians in sight?" Coulson asked.

"Negative sir." Hunter replied showing the tablet to him.

"It's upside down." Coulson said with matching hand gestures.

"Yeah right. Sorry." he tilted the tablet into the right position.

"You can see Donald Gill here." He pointed to one of the cameras.

"He looks like he's waiting for someone." Fitz notably said as Donnie looked left and right.

"I'm guessing it's not us." Coulson deadpanned.

"His motives still remain unclear at . Whoever he is meeting, we sure are going to meet them as well." Coulson added.

"So what do we do?" Fitz asked.

"Keep an eye on him. Do not approach him until his company arrives."

* * *

Everyone was at their posts keeping an eye for anyone who'll arrive.

There are some cars that passed. Some motor bike riders passed by. Two people walking at the street but one caught Barry's eye.

"Oh no. Iris!"

* * *

**A/N: Dun dun dun. I know I'm evil. There goes chapter 4. I hope you guys like it. I will try to find the time to upload another chapter. Thank you for your support. Mwah.**


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